Brake discs of the abovementioned type are known, e.g. from DE 10 2007 059 777 A1. In general, disc brakes of the relevant type are pneumatically and/or electromechanically actuable.
The adjustment nut can be rotated for adjustment. It has a pressure collar, the end face of which that faces the brake disc generally extends into the through-opening in the brake caliper, both when the brake is unactuated and when it is actuated. The through-opening can also be formed on a closure plate which sealingly closes the brake caliper or a sheet-metal cover of the caliper, which is referred to below merely as a “cover”.
The abovementioned through-opening is a functional opening for the passage of at least one pressure or adjustment spindle, which is fixed in terms of rotation but can be moved axially by means of the adjustment nut, wherein the axial movement or adjustment is used to compensate lining and/or disc wear. The adjustment spindle acts by means of one of its end sections against the brake lining on the application side.
The through-opening region in the cover for the adjustment spindle also serves as a seat for one or more seals. It is delimited by an encircling tubular collar which extends axially with respect to the interior of the brake and is adjoined by an inward-angled, radially aligned flange.
In the case of the brake according to DE 10 2007 059 777 A1, there are three differently arranged, shaped and acting (partial) seals for sealing the interior space of the caliper.
The first seal for sealing the annular space mentioned is formed by a flexible protective cap in the form of a folding boot, which is attached to the cover at one end and to a part of the adjustment spindle which faces the brake disc at the other end.
The second seal for sealing the annular space mentioned rests against the external thread of the adjustment spindle. It is held by a metal sleeve secured on the rotatable pressure collar of the adjustment nut. The metal sleeve extends radially inward to a point close to the external thread of the adjustment spindle in order to support the seal of flat design and stabilize it against twisting.
The third seal is secured on the cover and rests sealingly against the metal sleeve, thereby sealing the remainder of the annular space.
The third seal is thus situated in the radially outer part of the annular space, while the second seal is situated in the radially inner part.
Since the second seal and the metal ring are rotated for adjustment, whereas the adjustment spindle and the third seal are held fixed in terms of rotation, considerable friction forces occur during adjustment, namely between the second seal and the adjustment spindle, on the one hand, and the third seal and the metal sleeve, on the other hand. Since, furthermore, the second seal is rotated during adjustment, whereas the third seal is stationary during adjustment, the two seals cannot be combined in a single seal.